Field of the Invention
The present invention relates to a solid-state image sensor and image sensing system.
Description of the Related Art
FIG. 2 of Japanese Patent Laid-Open No. 2001-223566 shows a comparator including pixels 201, 202, and 203, a current path formation block 210, a current path 211, and a comparison unit 215. The current path formation block 210 includes MOS transistors 204, 205, and 206 having gates to which charge-voltage converters of the pixels 201, 202, and 203 are respectively connected. The current path 211 includes a MOS transistor having a gate to which a reference voltage 212 is supplied. The comparison unit 215 includes an arithmetic amplifier including the current path formation block 210 and current path 211 as a differential pair, and can obtain a digital signal corresponding to a pixel signal based on the output from the comparison unit 215.
In this arrangement shown in FIG. 2 of Japanese Patent Laid-Open No. 2001-223566, a transistor 213 which forms the differential pair together with the amplification transistors 204, 205, and 206 of the pixels 201, 202, and 203 is provided outside the pixels 201, 202, and 203. In an arrangement like this, it is difficult to improve the balance between one current path and the other current path forming the differential pair, and this sometimes makes it difficult to sufficiently increase the readout accuracy of a pixel signal.